Modern merchant ships are of such dimensions that the anchors appear quite small against their background. But how does it generally turn out that such structures hold a dry cargo ship or a tanker with a mass several thousand times greater?
Each anchor has a holding force factor. This parameter is the ratio of the weight that the anchor can carry to the weight of that anchor. In general, the coefficient values are different, but this indicator rarely exceeds 12 units.
The heaviest of all anchors produced in the world weighed 36 tons. This anchor was on the Seawise Giant tanker. The laden mass of this ship was more than 560,000 tons. However, if we multiply the mass of the anchor by the holding force factor (12), we get a number much smaller than the mass of the ship. So how did the anchor hold such a ship?
To understand this, two points must be taken into account. First, the anchor need not bear the weight of the ship at all, as it is compensated by Archimedes’ strength. That is, the anchor must simply resist wind and/or current forces that could move the ship. Therefore, when choosing an anchor for a ship, engineers are guided not by the size of the ship, but by its mass.
The second nuance is that the main role in holding the ship is played not by the anchor, but by the chain. In order for the ship to remain in place, it is necessary to lower a part of the chain to the bottom, the length of which will be 5-7 times greater than the depth of this place.
That is, due to the weight of the chain and the frictional force at the bottom of the chain, the ships stay in one place.
Source: Ferra
